Exemplary embodiments of the present invention relate generally to compact scanning phased array antenna devices.
Tightly Coupled Dipole Arrays (TCDAs) are frequently implemented as a result of their low profile, bandwidths up to 6:1, good scan performance, and low cross polarization characteristics. However, the dipole elements used in TCDAs are balanced structures, and as a result, the feed network for a TCDA must include baluns or 180° hybrids that can sustain array bandwidths of greater than 6:1.
The volume available for such a balun is limited, particularly for designs capable of operating at frequencies above 500 MHz. The known art has not been able to develop a passive balun that supports extremely wide bandwidths (>6:1) while fitting within the limited volume available in each unit cell (typically <λ/10 in linear dimension at low frequencies). As a result, the known art has not been able to obtain a compact antenna array with a small or low profile and desired performance.
Known TCDA designs use bulky external baluns or hybrids located below the ground plane of the TCDA structure, significantly increasing the total size, weight, and cost of the array. For example, a TCDA operating from 600-4500 MHz may have 30 mm separation (˜λ/17 at 600 MHz) between the dipoles and ground plane and the same distance between elements. Practical implementation of a wideband balun that physically fits within this available volume has been a problem, and known designs which physically fit within this available space yield bandwidths of less than 2:1.
An alternative technique, as described in U.S published patent application number 2012/0146869, forgoes baluns altogether and uses vias to mitigate common mode resonances, resulting in 3:1 bandwidth or 5:1 bandwidth with additional external baluns or hybrids located below the ground plane, significantly increasing the total size, weight, and cost of the array.
Described herein are embodiments of a novel design that overcomes such size and performance limitations by exploiting the natural reactance of a compact Marchand balun for use as an impedance matching network for each feed port, eliminating the need for external baluns without compromising the bandwidth of the array. By introducing a network that functions both as a balun and impedance matching network, the bandwidth of an exemplary embodiment of the array may be improved while simultaneously providing a standard 50 ohm unbalanced feed for each element of the array. Other embodiments may, for example, provide impedances in the range of about 25-200 ohm. Embodiments of these networks may be printed on the same substrate as the array itself, thus adding minimal additional cost. Because no external feed circuitry is required in such embodiments, balun/impedance matching networks may be integrated directly onto the substrate, enabling an extremely compact wideband electronically scanned array (ESA). The result is a simultaneous reduction in size and weight and improvement in bandwidth compared to other feeding techniques.
In addition to the novel features and advantages mentioned above, other benefits will be readily apparent from the following descriptions of the drawings and exemplary embodiments.